1. Field of the Invention
The present invention relates to a method for producing an organic insulating film used for insulation and coating in electronic devices such as IC, LSI and the like.
2. Description of Related Art
Recently, the shrinking design rule of IC, LSI and the like has led to increased interconnection delay caused by parasitic capacity in an insulation film. For solving interconnection delay, it is desired that an insulation film has lower dielectric constant. Consequently, notice is taken of an organic insulating film using an organic resin having lower dielectric constant in place of a conventionally used CVD film or a silica-based film such as a spin on glass (SOG) film and the like. For the organic insulating film, thermosetting resins which can form a network polymer structure by curing are used for the purpose of suppressing thermal distortion. Particularly, organic resins having an unsaturated group in the resin chain are regarded since the resulting organic insulating film has lower water absorption. However, in the above-mentioned organic insulating film, it has been difficult to date to obtain reproducibility of its electric property as compared with an SOG film. Further, in the organic insulation film, uniformity has sometimes occurred in film quality and film thickness after baking.
An object of the present invention is to provide a method for producing an organic insulating film having low dielectric constant stably on a substrate.
The present inventors have intensively studied and resultantly found that the above-mentioned object can be attained by producing an organic insulating film on a substrate under specific oxygen atmosphere and temperature condition, and have completed the present invention.
Namely, the present invention relates to a method for producing an organic insulating film comprising the steps of
coating a solution containing a dissolved organic resin having a structure of the following formula (1) on a substrate, and
exposing said coated substrate at a temperature of 200xc2x0 C. or more under an atmosphere of an oxygen partial pressure of 0.01 atm or less, 
wherein, each of R1 to R8 is independently selected from the group consisting of a hydrogen atom, fluorine atom, chlorine atom, bromine atom and iodine atom, alkyl groups having 1 to 10 carbon atoms, functional groups containing a double bond having 2 to 10 carbon atoms, functional groups containing a triple bond having 2 to 10 carbon atoms, a methoxy group, ethoxy group and propoxy group.
The present invention relates to a method for producing an organic insulating film comprising coating a solution containing a dissolved organic resin having a structure of the formula (1) on a substrate, then, exposing the above-mentioned substrate at a temperature of 200xc2x0 C. or more under an atmosphere of an oxygen partial pressure of 0.01 atm or less, preferably an oxygen partial pressure of 0.001 or less: 
wherein each of R1 to R8 is independently selected from the group consisting of a hydrogen atom, fluorine atom, chlorine atom, bromine atom and iodine atom, alkyl groups having 1 to 10 carbon atoms, functional groups containing a double bond having 2 to 10 carbon atoms, functional groups containing a triple bond having 2 to 10 carbon atoms, and a methoxy group, ethoxy group and propoxy group.
Further, it is preferable that at least one of R1 to R8 in the formula (1) is a functional group containing a double bond having 2 to 10 carbon atoms or a functional group containing a triple bond having 2 to 10 carbon atoms, since, in this case, the resulting organic insulating film gets lower dielectric constant. Examples of these functional groups include unsaturated hydrocarbon groups such as a vinyl group, allyl group, isopropenyl group, butenyl group, cyclohexenyl group, cyclooctenyl group, butadienyl group, cyclopentadienyl group, ethynyl group, propinyl group and the like. Further, a vinyldimethylsilyl group, vinyldiethylsilyl group, divinylmethylsilyl group, vinyloxy group, allyloxy group, vinylamino group, allylamino group and the like are listed.
The organic resin in the present invention is not particularly restricted providing a skeleton of the formula (1) is included in the polymer chain of the resin, and particularly, it is preferable that the polymer chain has a structure of the following formula (2), 
wherein, R1 to R8 are as defined in the formula (1). Each of Q1 to Q4 is independently selected from the group consisting of a hydrogen atom, fluorine atom, chlorine atom, bromine atom and iodine atom, alkyl groups having 1 to 10 carbon atoms, functional groups containing a double bond having 2 to 10 carbon atoms, functional groups containing a triple bond having 2 to 10 carbon atoms, and a methoxy group, ethoxy group and propoxy group. X is selected from a single bond, alkyl groups having 1 to 10 carbon atoms, an ether group, ester group, ketone group, sulfone group and amide group.
In the present invention, it is preferable that the temperature atmosphere is 200xc2x0 C. or more and is not more than the thermal decomposition temperature of an organic resin used.
In the present invention, the time of curing a substrate is preferably from 1 minute to 5 hours, further preferably from 15 minutes to 1 hour.
Further, the present invention relates to a method for producing an organic insulating film comprising coating on a substrate a solution containing a dissolved organic resin having a structure of the formula (1), then, curing the above-mentioned substrate under a temperature atmosphere of 200xc2x0 C. or more and {circle around (1)} under an inert gas atmosphere of an oxygen concentration of 1 vol % or less, and/or, {circle around (2)} under a pressure-reduced air atmosphere of 0.05 atm or less. It is preferable that, in the formula (1), at least one of R1 to R8 is a functional group containing a double bond having 2 to 10 carbon atoms or a functional group containing a triple bond having 2 to 10 carbon atoms.
In the present invention, it is preferable that the temperature atmosphere is 200xc2x0 C. or more and is not more than the thermal decomposition temperature of an organic resin used.
In the present invention, the time of curing a substrate is preferably from 1 minute to 5 hours, further preferably from 15 minutes to 1 hour.
Further, in the present invention, the above-mentioned substrate is preferably exposed {circle around (1)} under an inert gas atmosphere of an oxygen concentration of 1 vol % or less, and/or, {circle around (2)} under a pressure-reduced air atmosphere of 0.005 atm or less.
The atmosphere {circle around (1)} and the atmosphere maybe applied alone or in combination. Further, a substrate may be exposed under the atmosphere {circle around (1)}, then, exposed under the atmosphere {circle around (2)}, under a temperature atmosphere of 200xc2x0 C. or more, alternatively, a substrate may be cured under the atmosphere {circle around (2)}, then, exposed under the atmosphere {circle around (1)}, under a temperature atmosphere of 200xc2x0 C. or more.
The condition {circle around (2)} that under a pressure-reduced air atmosphere of 0.05 atm or less is excellent for a method of forming stably an organic insulating film. For the purpose of improving throughput, the condition {circle around (1)} that under an inert gas atmosphere of an oxygen concentration of 1 vol % or less is preferable.
As the method for attaining the above-mentioned atmosphere {circle around (1)}, an inert gas film-separating method, and a method using a reducing agent are listed. By these methods, the oxygen concentration can be controlled. The oxygen concentration can be measured by a method in which an industrially used oxygen detector is connected to a gas line used, or a method in which an atmosphere gas is sampled by any method and analyzed by gas chromatography.
In the present invention, as the method for exposing a substrate under an atmosphere of 200xc2x0 C. or more, a substrate may advantageously be cured for example under an atmosphere heated to 200xc2x0 C. or more, and this method is not particularly restricted. As the method for producing such an atmosphere, a heating method using a hot plate which is used generally for electronic devices, a heating method using a furnace, and a heating method using irradiation of light such as RTP and the like, are listed. As the heating method used in the present invention, the method using a furnace is preferable particularly since the apparatus is simple and temperature control is easy.
As the inert gas used in the present invention, for example, nitrogen, helium, neon, argon, krypton, xenon and the like are listed, and industrially cheap nitrogen is preferable.
In forming an organic insulating film, particularly the atmosphere is not restricted in the heating treatment of a substrate in the pre-step at less than 200xc2x0 C. Specifically, a substrate may be pre-baked under an atmosphere of less than 200xc2x0 C. under the condition of exposure of the substrate to air.
By a method for producing an organic insulating film of the present invention, an organic insulating film having low dielectric constant can be stably formed on a substrate.
According to the present invention, an organic insulating film having low dielectric constant can be stably obtained.